The present invention relates to a method and to a system for the terminal-phase guidance of an interceptor missile towards a moving aerial target.
It is known that the trajectory of an interceptor missile towards an aerial target includes several successive phases, in particular a launch phase, an intermediate phase and a terminal phase. While the guidance during the launch and intermediate phases are important for successful interception, the terminal-phase guidance is even more important since it is this guidance that determines the shortest distance for the interceptor missile to approach said target and thus the probability of the target being destroyed. In the technology for guiding the interceptor missiles, this shortest approach distance is generally referred to as the “closest point of approach”.
In the prior art in general, an interceptor missile is guided in the terminal phase by “proportional navigation”, i.e. proportionally to the apparent rotation of the straight line (sight line) linking the interceptor missile to said target. Guidance of this type is disadvantageous in that the acceleration of the interceptor missile and the acceleration of the target are assumed to be zero. Therefore, if this assumption does not prove to be true (which is often with case with highly manoeuvrable targets), the closest point of approach actually achieved cannot be the best one.
To overcome a drawback of this kind, this known technology can include specific variants that make it possible, for example, to:
compensate for a constant acceleration limit in the manoeuvring of either the interceptor missile or the target,
compensate for a helical manoeuvre by the target, or
compensate for the steering time constant of the interceptor missile.
In turn, specific variants of this kind are disadvantageous in that they are analytical and have to be calculated and saved beforehand in the guidance system of the interceptor missile.
In addition, each of these specific variants is only effective in the exact situation for which it has been developed, and cannot be directly combined with another to optimise the closest point of approach between an interceptor missile and a target that are in a situation resulting from the combination of the respective specific situations.
Therefore, the actual dynamic manoeuvring between the interceptor missile and the target generally cannot correspond to any of these variants or to combinations thereof.
Furthermore, the article “Decision Directed Adaptive Estimation and Guidance for an Interception Endgame” by Dany Dionne, Hannah Michaïska, Joseph Shinar and Yaakov Oshman in the “Journal of Guidance, Control and Dynamics”, vol. 29, no. 4, July-August 2006 describes a terminal-phase guidance system in which the interceptor missile comprises a set of (Kalman filter-like) state estimators, a set of analytical guidance laws saved beforehand in said interceptor missile, and a decision unit for determining which of the predetermined guidance laws to implement on the basis of the measurements from said state estimator devices.
Therefore, this known guidance system includes the drawbacks mentioned above in relation to the specific variants for proportional navigation guidance.
In addition, this known guidance system also assumes that no external force is exerted on the interceptor missile, nor on the target until the point of interception
Similarly, US 2004/155142 A1 uses a guidance law saved beforehand, the analytical expression of which is given by a plurality of equations.
The article “Using a multiple-model adaptive estimator in a random evasion missile/aircraft encounter” by Yaakov Oshman, Joseph Shinar and S. Avrashi Weizman in the “Journal of Guidance, Control and Dynamics”, vol. 24, no. 6, November-December 2001 describes a DGL guidance law that implies no acceleration of the interceptor missile and no manoeuvring of the target.